Anaerobic bacteria digest animal waste to produce biogas, which is subsequently burnt as fuel. How are these two processes classified?

Correct Option

The correct option is

Both digestion and burning are chemical changes.

Explanation

A chemical change is a process where one or more substances are transformed into new substances with different chemical properties. These changes involve the breaking and making of chemical bonds and are generally irreversible. In contrast, a physical change affects the form of a chemical substance, but not its chemical composition.

Process Analysis

• Anaerobic Digestion: In this process, anaerobic bacteria break down complex organic matter present in animal waste into simpler substances, primarily methane ($CH_4$) and carbon dioxide ($CO_2$). Since the original organic material is converted into entirely new substances, this is a chemical change.
• Burning of Biogas: Burning, or combustion, is an oxidation reaction where the fuel (biogas) reacts with oxygen to produce carbon dioxide, water vapor, heat, and light. As new chemical products are formed and the process cannot be reversed to retrieve the original biogas, this is also a chemical change.

Key Takeaway: Both the biological decomposition of waste and the combustion of fuel involve the formation of new substances, classifying both processes as chemical changes.